Impact of Photon Counting Detector CT Derived Virtual Monoenergetic Images on the Diagnosis of Pulmonary Embolism

Abstract

Purpose: To assess the impact of virtual-monoenergetic-image (VMI) energies on the diagnosis of pulmonary embolism (PE) in photon-counting-detector computed-tomography (PCD-CT). Methods: Eighty patients (median age 60.4 years) with suspected PE were retrospectively included. Scans were performed on PCD-CT in the multi-energy mode at 120 kV. VMIs from 40–70 keV in 10 keV intervals were reconstructed. CT-attenuation was measured in the pulmonary trunk and the main branches of the pulmonary artery. Signal-to-noise (SNR) ratio was calculated. Two radiologists evaluated subjective-image-quality (noise, vessel-attenuation and sharpness; five-point-Likert-scale, non-diagnostic–excellent), the presence of hardening artefacts and presence/visibility of PE. Results: Signal was highest at the lowest evaluated VMI (40 keV; 1053.50 HU); image noise was lowest at the highest VMI (70 keV; 15.60 HU). Highest SNR was achieved at the lowest VMI (p < 0.05). Inter-reader-agreement for subjective analysis was fair to excellent (k = 0.373–1.000; p < 0.001). Scores for vessel-attenuation and sharpness were highest at 40 keV (both:5, range 4/3–5; k = 1.000); scores for image-noise were highest at 70 keV (4, range 3–5). The highest number of hardening artifacts were reported at 40 keV (n = 22; 28%). PE-visualization was rated best at 50 keV (4.7; range 4–5) and decreased with increasing VMI-energy (r = −0.558; p < 0.001). Conclusions: While SNR was best at 40 keV, subjective PE visibility was rated highest at 50 keV, potentially owing to the lower image noise and hardening artefacts.

Technical Basics and Clinical Benefits of Photon-Counting CT

“…In PCD-CT examinations of 80 patients with suspected pulmonary embolism (PE), subjective PE visibility was rated highest in VMIs at 50 keV. 64 For coronary CTA, VMIs at 40 keV were preferred when combined with high levels of iterative reconstruction (QIR 3 and QIR 4) both in a phantom evaluation and in a study of 10 patients. 65 Meanwhile, the possibility of contrast agent reduction when using VMIs at low energy has been investigated.…”

“…In a comparative study of 39 patients undergoing contrast-enhanced abdominal PCD-CT in the portal-venous phase, 63 the authors found optimal results with standardized reconstructions of VMIs at 50 keV, which showed significantly higher CNR at the same radiation dose with similar subjective image quality compared with EID-CT. Figure 10 shows a clinical example of an abdominal CT scan. In PCD-CT examinations of 80 patients with suspected pulmonary embolism (PE), subjective PE visibility was rated highest in VMIs at 50 keV 64 . For coronary CTA, VMIs at 40 keV were preferred when combined with high levels of iterative reconstruction (QIR 3 and QIR 4) both in a phantom evaluation and in a study of 10 patients 65 …”

Virtual Monoenergetic Imaging of Thoracoabdominal CTA on a Photon-Counting Detector CT: Assessment of Image Quality and Leveraging Low-keV Series for Salvaging Suboptimal Contrast Acquisitions

“…Whether a previous measurement of the cardiovascular circulation time or a general increase in the delay between the contrast injection and the scan is the answer to this problem needs to be investigated. The noise level reduction in low keV VMIs on a PCD-CT compared to a EID-CT has been shown in multiple studies and examined body parts [22,30]. In addition, the rst studies have been published that combined increase of attenuation of low keV reconstructions with noise reduction on PCD-CT to reduce the amount of the iodine load.…”

Optimisation of virtual monoenergetic reconstructions for the diagnosis of pulmonary embolism using photon-counting detector computed tomography angiography

“…As far as the authors are aware, as of the current date, only one investigation (Yalynska et al .) has been conducted on PCD-CT using different image reconstruction parameters, including a 2-mm slice thickness and keV values ranging from 40 to 70 keV [ 29 ]. Yalynska et al .…”